One problem with known spray apparatus is that many liquid chemical mixtures or compositions to be applied to crops or to weeds may not be true solutions and often comprise a chemical or mixture of chemicals and a bulky powdered filler e.g. of chalk. Such materials tend to deposit a sediment in the spray apparatus unless continually agitated. Such sediment may be detrimental to the operation of the spray apparatus or may simply require removal in a time wasting operation.
To promote agitation of liquid spray materials it is known to provide an agricultural spray apparatus comprising a liquid chemical holding tank, a boom formed with spray nozzles along its length, a pump for forcing liquid from the tank to the nozzles, and conduits (hereafter lines) connecting the tank, pump and nozzles, with a return line from the spray nozzles to the holding tank. A disadvantage of such apparatus is that it is then difficult accurately to meter the amount of liquid spray material applied to the field by the apparatus since the metering device depends on measuring flow rate and thus needs to take account of the quantity of liquid which is returned from the nozzles to the tank.
Another problem with known spray apparatus is that dripping of liquid spray material from the nozzles tends to occur after spraying has been discontinued. Such dripping is wasteful of chemical and potentially harmful to plants, animals and to the spray operator. It is thus known to apply vacuum to the lines of a spray apparatus when spraying is discontinued to assist the operation of anti-drip valves, i.e. diaphragm check valves provided in the lines at the spray nozzles.
A further disadvantage with known spray apparatus is that it is often necessary to wash out the sprayer, e.g. the spray lines and tank after use, usually with clean water, to prevent clogging of the lines of the sprayer, but it is not possible subsequently to remove the water from the lines except by displacing the water with liquid to be sprayed when the sprayer is next used. Thus when the operator first uses the spray apparatus after cleaning he must run the sprayer for a period of time, usually while stationary, to displace the water from the lines before commencing spraying. However if the operator runs the sprayer for too long a period of time while stationary, liquid spray will be wasted and the headland of the field will be contaminated with the heavy concentration of spray. It is thus common to find such "burnt" patches often next to hedgerows or ditches in fields and the environmental implications are clearly apparent. If, alternatively, the operator starts spraying before all of the cleaning water has been displaced from the spray lines, a part of the field will not be effectively treated by the spray.
An object of the invention is to provide improved means for agitating liquid spray mixtures in the sprayer device. Preferably this agitation will happen automatically i.e. without the need for intervention by the operator, e.g. constantly or when spraying ceases. Preferably the agitation will also occur when the spray apparatus is being filled.
It is a another object of the invention to provide means for preventing or mitigating dripping from the spray nozzles.
It is a further object of the invention to provide means for purging the lines of the sprayer of cleaning or other liquid after use to permit immediate start-up without the need to exhaust cleaning water from the lines.